PREFACE THE leisure and incentive to prepare for the press the lectures which form this book I owe to an invitation from Dean Russell of Teachers' College, Columbia University, New York City, to spend the session 1923-24 there as Visiting Professor of Education. To him, and to Dr. E. L. Thorndike, at whose suggestion the invitation was extended to me, I owe a debt which I am glad to acknowledge; and no less to Sir Theodore Morison and the Council of Armstrong College in Newcastle for acquiescence in the necessary leave of absence, made possible by the great kindness of my predecessor and old friend, Mark B« Wright, in emerging from his retirement to take up for another year his former duties The lectures were three times delivered, in the winter, spring, and summer semesters, .and are here printed sub- stantially as given on the last occasion. Any merits they may have they owe to my audiences, for from a class ranging in age from nineteen to fifty-five years, possessed of teaching experience of every conceivable sort, and gathered not only from every State of the Union, but from every continent, the teacher could not fail to learn, whatever they may have learned from him. And to them, to " 251 C/' I dedicate the present volume.